Rhizobium is a type of bacterium that lives in soil and around and inside of the roots of certain plants (legumes). This is Rhizobium in its free-living state in soil, surrounded by a halo of protective covering called a capsule. The slimy capsule, made of exopolysaccharide, protects rhizobium from drying out. It also helps the bacterium stick to root hairs during other stages of its life cycle, when rhizobium forms a symbiotic partnership with plants like clover.

The image to the right is an animated GIF which shows the size of Rhizobium trifolii in comparison to other microorganisms. The animated GIF file is large (450 K), so it will take a while to download if you are connected via a modem.